The present invention relates to rolls for use in calenders or like machines, and more particularly to improvements in rolls of the type wherein a cylindrical shell spacedly surrounds a stationary carrier and is supported by a row of bearing elements which, in turn, are supported by the carrier. Still more particularly, the invention relates to improvements in a roll wherein the bearing elements are adjustable relative to the carrier by fluid-operated pressure generating devices so as to prevent or to compensate for deformation of the shell in response to pressure which is applied thereto by a running web of the material to be treated, by a complementary roll or by a non-rotating body.
Rolls of the above outlined character are used in a variety of machines including calenders, presses for paper or cellulose, printing machines, rolling mills for steel, plastic or the like, as well as glazing machines.
German Offenlegungsschrift No. 26 08 646 discloses a roll wherein the carrier supports a row of spaced-apart bearing elements for the rotary shell and each bearing element is movable relative to the carrier by a discrete pressure generating device in the form of a fluid-operated motor. The purpose of the bearing elements is to reduce the extent of flexing of the shell under pressure and/or to uniformize the pressure between the roll and a complementary roll or the like. Each pressure generating device comprises a plunger which is fixed to the carrier and extends into a cylinder chamber of the corresponding bearing element, or a cylinder which is fixed to the carrier and defines a cylinder chamber for a plunger which is secured to the respective bearing element. The bearing elements have convex surfaces of circular or polygonal outline, and such surfaces are adjacent to the internal surface of the shell. If the convex surfaces of the bearing elements have a rectangular outline, their longer sides are parallel with the axis of the shell. As a rule, each convex surface is formed with four pockets or recesses which receive pressurized fluid from the respective cylinder chamber and are separated from each other by a pair of intersecting ribs which together form a substantially cruciform land. The pockets form part of a hydrostatic seal between the bearing element and the cylindrical internal surface of the rotary shell. The flow of fluid from the cylinder chamber of a pressure generating device into the pockets of the respective bearing element is throttled, e.g., by forming the bearing element with a flow restricting passage, channel or bore which connects the pockets with the cylinder chamber.
If the aforementioned convex surfaces of the bearing elements have a rectangular outline, with the longer sides parallel to the axis of the shell and with the shorter sides extending in the circumferential direction of the shell, the magnitude of forces which develop between the bearing elements and the shell varies very little or not at all, as considered in the axial direction of the roll. Otherwise stated, the magnitude of forces which act between a given bearing element and the adjacent portion of internal surface of the shell is constant, as considered in the axial direction of the shell. The magnitude of such forces varies much more when the concave surfaces of the bearing elements have a circular outline. Moreover, and since the pressure of fluid in the cylinder chambers of the pressure generating devices cannot be increased at will, the magnitude of forces acting upon the shell per unit length of the roll is also limited, i.e., a conventional roll cannot compensate for any and all pressures which are exerted upon and tend to flex the shell when the roll is in actual use in a calender, rolling mill or the like.